FI70438C - FOERFARANDE FOER REGLERING AV MEKANISK SLIPNING AV TRAE - Google Patents

Description

χ 70438 METHOD FOR CONTROLLING THE MECHANICAL GRINDING OF WOOD - FÖRFARANDE FÖR REGLERING AV MEKANISK SLIPNING AV TRÄ

The invention relates to a method for controlling mechanical stone grinding and / or pressure grinding of wood.

The control of the mechanical grinding of wood is hampered by the ever-changing quality of the wood as well as the ever-changing surface properties of the grindstone. The quality of the wood depends, on the one hand, on the part of the tree trunk or growing area from which the log to be sanded comes, and, on the other hand, on how the wood has been treated before sanding.

In terms of the grinding result, the aim is to obtain as uniform a CF number as possible for the groundwood. In order to obtain as uniform a CF number as possible for the groundwood, it is already known to control grinding, e.g. so that the hydraulic pressure controlling the wood supply is kept constant, whereby the wood feed rate (production) and the load of the drive motor 15 vary according to the situation; alternatively, the feed rate of the wood is kept constant, in which case the above-mentioned hydraulic pressure must be varied according to the situation, and the load of the drive motor varies. Furthermore, it is known to control the grinding so that the load of the drive motor is kept constant, in which case, for example, the above-mentioned hydraulic pressure must be varied according to the situation and the feed rate of the wood varies. In practice, however, the control constants have to be changed as the condition of the grindstone deteriorates over time. In general, it can be said that currently known control methods for controlling wood grinding are unsatisfactory, and scorched control methods do not provide a sufficiently uniform grinding quality.

It is an object of the present invention to obviate the above drawbacks. In particular, it is an object of the invention to provide a new method for controlling the mechanical grinding of wood so that quantities characterizing the properties of the sand, such as CF number, reject content, penetration resistance and tear index, and the specific grinding energy requirement can be adjusted in a controlled manner.

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With regard to the features characteristic of the invention, reference is made to the claims.

The invention is based on a thorough theoretical analysis of the sanding event, which led to a new quantity, wood plasticity (\\), which in controlled laboratory experiments was found to be suitable in many respects as a mechanical sanding control variable, especially when said quantity often unambiguously explains e.g. the specific grinding energy demand 10 and the CF number of the grind.

The invention will now be described in detail with reference to a diagram and exemplary embodiments with reference to the accompanying drawings, in which Figure 1 shows a reduced grinding process, Figure 2 shows the specific production of groundwood as a function of wood plasticity, Figure 3 shows specific as a function, Fig. 5 shows the reject content of the groundwood as a function of wood plasticity, Fig. 6 shows the infiltration resistance of the groundwood as a function of wood plasticity, Fig. 7 shows the original wet strength of the groundwood as a function of wood plasticity, and Fig. 8 shows groundwood tear index as a function of wood plasticity.

Reference is now made to Figure 1, which shows the grinding-30 event in a reduced form. In the figure, the wood 1 is pressed by a force F against the surface of a rotating stone 2, the nose of which moves at a circumferential speed w. In order for the circumferential velocity w of the stone 2 to remain at said value, a torque force F must be applied to the stone, the magnitude of which depends on the properties of the wood and water layers between the wood 1 and the stone 2. The combined effect of these layers on grinding is described by a quantity called the plasticity η of the wood. If we search for the independent factors of wood grinding speed or 70438 3 that, when changing one by one, affect the grinding speed while all other independent factors remain constant at the same time, the general equation (II) is obtained.

V - f (1, s, F, n) II

3 5 where V is the wood sanding speed, () m / s; 1 is the length of the tree, () m; s is the line of contact between the wood and the stone in the overturning direction of the grinding stone, i.e. the grinding distance, () m; F is the compressive force of the wood 2 against the rotating stone, () N, ia η is the plasticity of the wood, () Ns / m.

According to the invention, it has been found that the plasticity 10 follows Equation III

n = k · —— m vs where n is the plasticity of the wood (under certain sanding conditions); k is a dimensionless constant; v is the wood feed rate, () m / s; and F and s are as above.

The quantity F / v-s, which describes the plasticity of wood, and the components F and v of which are easily measurable in practice, was tested experimentally as a control parameter for the mechanical grinding of wood. For this purpose, laboratory grinding of spruce wood was performed under well-controlled conditions, eliminating variations in wood quality and abrasive surface properties. In grinding, the circumferential speed of the grindstone was 3.5; 7; 15 or 30 m / s, and during each grinding the compressive force was constant. These factors determined the feed rate of the wood or the specific production of the chips, the plasticity of the wood, the specific need for sanding energy and the properties of the chips: CF number, reject content, infiltration resistance, initial wet strength and tear index. The measurement results are shown graphically in Figures 2-8 as a function of the new grinding control parameter, i.e. the plasticity of the wood.

It can be seen from the measurement results that said control parameter, the plasticity of the wood, in the studied area correlates in a straight line with all the above-mentioned 70438 4 indicators except for the specific production and the original wet strength.

The conclusion from the research results is that by choosing the quantity F / vs in a certain driving situation 5 (wood quality, grinding stone surface properties and grinding stone circumferential speed are constant) an unambiguous result is obtained, e.g.

with respect to the CF number of the groundwood.

The embodiments are intended to illustrate the invention without limiting it in any way, and embodiments of the invention may vary within the scope of the appended claims.

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II

Claims (8)

70438 A method for controlling mechanical stone grinding and / or pressure grinding of wood, characterized in that the control parameter used is a Suur-retta describing the plasticity of wood according to formula (I) 5 n = - - (I) vs where F is the compressive force of wood against rotating stone, v is wood grinding speed and s is the grinding distance. Method according to Claim 1, characterized in that the circumferential speed (w) 10 of the grinding stone is kept constant. Method according to Claim 1 or 2, characterized in that the characteristic grinding energy requirement is adjusted by adjusting the plasticity (η) of the wood. Method according to one of Claims 1 to 3, characterized in that the CF value of the groundwood is adjusted by adjusting the plasticity (η) of the wood. Method according to one of Claims 1 to 4, characterized in that the reject content of the groundwood is adjusted by adjusting the plasticity (η) of the wood. Method according to one of Claims 1 to 5, characterized in that the infiltration resistance of the groundwood is adjusted by adjusting the plasticity (η) of the wood. Method according to one of Claims 1 to 6, characterized in that the tear index of the groundwood is adjusted by adjusting the plasticity (η) of the wood. Method according to one of Claims 1 to 7, characterized in that the plasticity of the wood is kept substantially constant during sanding. 30 6 70438